function updatebudget() {
	var budget = currentBudget;

	if(document.getElementById('driver1').value > 0)
		budget = budget - drivervalues[document.getElementById('driver1').value];
	if(document.getElementById('driver2').value > 0)
		budget = budget - drivervalues[document.getElementById('driver2').value];
	if(document.getElementById('testdriver').value > 0)
		budget = budget - drivervalues[document.getElementById('testdriver').value];
	if(document.getElementById('constructorID').value > 0)
		budget = budget - constructorvalues[document.getElementById('constructorID').value];

	if(document.getElementById('driver1').value > 0 && document.getElementById('driver2').value > 0) {
		if(document.getElementById('driver1').value == document.getElementById('driver2').value || document.getElementById('driver1').value == document.getElementById('testdriver') || document.getElementById('testdriver').value == document.getElementById('driver2'))
			alert('Je mag dezelfde rijder maar één keer selecteren');
	}

	document.getElementById('budgetspan').innerHTML = addCommas(budget);
	if(budget < 0)
		alert('Met deze aankoop heb je zojuist je budget overschreden');
}

function addCommas(nStr)
{
	nStr += '';
	x = nStr.split('.');
	x1 = x[0];
	x2 = x.length > 1 ? '.' + x[1] : '';
	var rgx = /(\d+)(\d{3})/;
	while (rgx.test(x1)) {
		x1 = x1.replace(rgx, '$1' + '.' + '$2');
	}
	return x1 + x2;
}